24,25-Dihydroxyvitamin D3 administration increases incidence of parturient paresis

Fifty percent (7/14) of aged cows treated with 4 mg 24,25-dihydroxyvitamin D3 intramuscularly precalving developed parturient paresis shortly after calving compared with 7% (1/14) of controls. Injection of 24,25-dihydroxyvitamin D3 increased concentrations in blood plasma 15 times that in control cows. Blood plasma 1,25-dihydroxyvitamin D concentrations were elevated in all groups on day of calving but were not different. Injection of 24,25-dihydroxyvitamin D3 did not alter the typical plasma profile for calcium, phosphorus, or 1,25-dihydroxyvitamin D of paretic or nonparetic cows around parturition. Although injection of 24,25-dihydroxyvitamin D3 was associated with an increased incidence of parturient paresis, the mechanism remains unknown.